Liquid crystal display with sub pixel regions defined by sub electrode regions

ABSTRACT

A liquid crystal display device includes a first substrate; a second substrate; and a liquid crystal layer interposed between the first substrate and the second substrate and having liquid crystal molecules therein. The first substrate includes a first electrode facing the liquid crystal layer. The second substrate includes a second electrode facing the liquid crystal layer. The first electrode, the second electrode, and a region of the liquid crystal layer supplied with a voltage by the first electrode and the second electrode define a pixel region which is a unit for display. The pixel region includes a plurality of sub pixel regions, in each of which the liquid crystal molecules are aligned in an axial symmetrical manner. At least one of the first electrode and the second electrode includes a plurality of openings, which are regularly arranged, in the pixel region. The at least one of the first electrode and the second electrode having the openings include a plurality of polygonal sub electrode regions, each of which has at least a part of the plurality of openings at least one of at corners and along and overlapping sides thereof. The plurality of sub pixel electrodes are defined by the sub electrode regions.

This application is a continuation of application Ser. No. 09/357,814,filed Jul. 20, 1999 now U.S. Pat. No. 6,384,889, the entire content ofwhich is hereby incorporated by reference in this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device usedfor a monitor of, for example, computers, wordprocessors, car navigationsystems, and TVs, and a method for producing the same.

2. Description of the Related Art

Today, TN (twisted nematic) liquid crystal display devices (hereinafter,referred to as “LCD devices”) are in wide use. In a TN LCD device, upperand lower alignment layers are treated by rubbing in differentdirections from each other, so that liquid crystal molecules are in atwisted alignment in the state where no voltage is applied. The TN LCDdevice has problems of a gray scale inversion phenomenon and anexcessive dependency of the display quality on the viewing angle.

In order to solve such problems, a liquid crystal material having anegative dielectric anisotropy and a vertical alignment mode which usesa vertical alignment layer has been proposed. The vertical alignmentmode provides a black display when no voltage is applied. A satisfactoryblack display is obtained in a quite large viewing angle range by using,for example, a phase plate having a negative refractive indexanisotropy. The use of such a phase plate substantially compensates forbirefringence caused by a liquid crystal layer in which the liquidcrystal molecules are vertically aligned when no voltage is applied. Inthis manner, a high contrast display is realized in a wide viewing anglerange. However, the vertical alignment mode has the problem of a grayscale inversion phenomenon which is observed in a direction identicalwith the direction in which the liquid crystal molecules are tilted whena voltage is applied.

Japanese Laid-Open Publication No. 6-301036 discloses an LCD devicehaving an opening at a center of an area of a counter electrode, thearea corresponding to a pixel electrode. Such a structure causes anelectric field between the pixel electrode, and the counter electrode tobe inclined with respect to surfaces thereof, whereas the electric fieldis vertical with respect to the surfaces without such a structure.Accordingly, when a voltage is applied in the vertical alignment mode,the liquid crystal molecules are tilted in an axially symmetricalmanner. The dependency of the display quality on the viewing angle ofsuch an LCD device is averaged in all azimuth directions when comparedwith an LCD device in which the liquid crystal molecules are tilted inone direction. As a result, the LCD device disclosed in theabove-mentioned publication provides a quite satisfactory viewing anglecharacteristic.

Japanese Laid-Open Publication No. 8-341590 discloses an LCD devicehaving a projection surrounding a pixel region or divided pixel regionand also an alignment fixing layer. Such a structure defines theposition and the size of the liquid crystal region in which the liquidcrystal molecules are aligned in an axially symmetrical manner, andstabilizes the axially symmetric alignment of the liquid crystalmolecules.

However, the structure disclosed in Japanese Laid-Open Publication No.6-301036 makes it difficult to generate an electric field inclined withrespect to the electrode surface uniformly in the entirety of pixelregions. As a result, the liquid crystal molecules respond to theapplication of the voltage in a delayed manner in a part of the pixelregions, which results in an image sticking phenomenon.

The structure disclosed in Japanese Laid-Open Publication No. 8-341590requires a projections to be formed of a resist or the like on a baseplate. This increases the number of production steps and thus raisescosts.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a liquid crystal displaydevice includes a first substrate; a second substrate; and a liquidcrystal layer interposed between the first substrate and the secondsubstrate and having liquid crystal molecules therein. The firstsubstrate includes a first electrode facing the liquid crystal layer.The second substrate includes a second electrode facing the liquidcrystal layer. The first electrode, the second electrode, and a regionof the liquid crystal layer supplied with a voltage by the firstelectrode and the second electrode define a pixel region which is a unitfor display. The pixel region includes a plurality of sub pixel regions,in each of which the liquid crystal molecules are aligned in an axialsymmetrical manner. At least one of the first electrode and the secondelectrode includes a plurality of openings, which are regularlyarranged, in the pixel region. The at least one of the first electrodeand the second electrode having the openings include a plurality ofpolygonal sub electrode regions, each of which has at least a part ofthe plurality of openings at least one of at corners and along andoverlapping sides thereof. The plurality of sub pixel electrode s aredefined by the sub electrode regions.

In one embodiment of the invention, the first electrode includes aplurality of pixel electrodes arranged in a matrix, and the plurality ofpixel electrodes are each connected to a scanning line and a signal linethrough a switching device. The second electrode is a counter electrodefacing the plurality of pixel electrodes.

The plurality of pixel electrodes each have at least one of theplurality of sub electrode regions.

In one embodiment of the invention, at least two of the plurality of subelectrode regions are congruent polygons to each other and share acommon side.

In one embodiment of the invention, the polygons each have rotationarysymmetry, and the liquid crystal molecules are aligned in an axiallysymmetrical manner with respect to an axis for the rotationary symmetryof the polygons.

In one embodiment of the invention, at least two of the plurality of subelectrode regions are polygons sharing a common side, and the openingsare at least 2 μm away from an edge of the pixel electrode.

In one embodiment of the invention, the polygons are congruent to eachother.

In one embodiment of the invention, the polygons each have rotationarysymmetry, and the liquid crystal molecules are aligned in an axiallysymmetrical manner with respect to an axis for the rotationary symmetryof the polygons.

In one embodiment of the invention, the liquid crystal layer is formedof a liquid crystal material having a negative dielectric anisotropy,and the liquid crystal molecules of the liquid crystal material arealigned substantially vertically with respect to surfaces of the firstsubstrate and the second substrate in the state where no voltage isapplied.

In one embodiment of the invention, at least one of the first substrateand the second substrate includes a column-like projection, forcontrolling the thickness of the liquid crystal layer, outside the pixelregion.

In one embodiment of the invention, the liquid crystal layer includes achiral dopant, and the liquid crystal molecules have a spiral pitchwhich is about four times the thickness of the liquid crystal layer.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga negative refractive index anisotropy.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga positive refractive index anisotropy

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one biaxial phase plate at leastone of between the first substrate and the polarizer closer to the firstsubstrate than to the second substrate and between the second substrateand the polarizer closer to the second substrate than to the firstsubstrate

In one embodiment of the invention, at least two of the plurality of subelectrode regions are polygons sharing a common side, and at least oneof sides of at least one of the sub electrode regions matches at leastone of edges of the pixel electrode.

In one embodiment of the invention, the polygons are congruent to eachother.

In one embodiment of the invention, the polygons each have rotationarysymmetry, and the liquid crystal molecules are aligned in an axiallysymmetrical manner with respect to an axis for the rotationary symmetryof the polygons.

In one embodiment of the invention, the liquid crystal layer is formedof a liquid crystal material having a negative dielectric anisotropy,and the liquid crystal molecules of the liquid crystal material arealigned substantially vertically with respect to surfaces of the firstsubstrate and the second substrate in the state where no voltage isapplied.

In one embodiment of the invention, at least one of the first substrateand the second substrate includes a column-like projection, forcontrolling the thickness of the liquid crystal layer, outside the pixelregion.

In one embodiment of the invention, the liquid crystal layer includes achiral dopant, and the liquid crystal molecules have a spiral pitchwhich is about four times the thickness of the liquid crystal layer.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga negative refractive index anisotropy at least one of between the firstsubstrate and the polarizer closer to the first substrate than to thesecond substrate and between the second substrate and the polarizercloser to the second substrate than to the first substrate.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga positive refractive index anisotropy at least one of between the firstsubstrate and the polarizer closer to the first substrate than to thesecond substrate and between the second substrate and the polarizercloser to the second substrate than to the first substrate.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one biaxial phase plate at leastone of between the first substrate and the polarizer closer to the firstsubstrate than to the second substrate and between the second substrateand the polarizer closer to the second substrate than to the firstsubstrate.

In one embodiment of the invention, at least one of the first substrateand the second substrate has an alignment fixing layer, for controllingthe axial symmetrical alignment of the liquid crystal molecules, betweenthe liquid crystal layer and at least one of the first electrode and thesecond electrode.

In one embodiment of the invention, the first electrode includes aplurality of pixel electrodes arranged in a matrix, and the plurality ofpixel electrodes are each connected to a scanning line and a signal linethrough a switching device. The second electrode is a counter electrodefacing the plurality of pixel electrodes.

The plurality of pixel electrodes each have at least one of theplurality of sub electrode regions.

In one embodiment of the invention, at least two of the plurality of subelectrode regions are congruent polygons to each other and share acommon side.

In one embodiment of the invention, the polygons each have rotationarysymmetry, and the liquid crystal molecules are aligned in an axiallysymmetrical manner with respect to an axis for the rotationary symmetryof

In one embodiment of the invention, at least one of the first substrateand the second substrate includes a column-like projection, forcontrolling the thickness of the liquid crystal layer, outside the pixelregion.

In one embodiment of the invention, the liquid crystal layer is formedof a liquid crystal material having a negative dielectric anisotropy,and the liquid crystal molecules of the liquid crystal material arealigned substantially vertically with respect to surfaces of the firstsubstrate and the second substrate in the state where no voltage isapplied.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga negative refractive index anisotropy.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga positive refractive index anisotropy.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one biaxial phase plate at leastone of between the first substrate and the polarizer closer to the firstsubstrate than to the second substrate and between the second substrateand the polarizer closer to the second substrate-than to the firstsubstrate.

In one embodiment of the invention, the liquid crystal layer includes achiral dopant, and the liquid crystal molecules have a spiral pitchwhich is about four times the thickness of the liquid crystal layer.

In one embodiment of the invention, at least one of the first electrodeand the second, electrode has a plurality of recessed portions which areregularly arranged.

In one embodiment of the invention, at least one of the first substrateand the second substrate includes a column-like projection, forcontrolling the thickness of the liquid crystal layer.

In one embodiment of the invention, the liquid crystal layer is formedof a liquid crystal material having a negative dielectric anisotropy,and the liquid crystal molecules of the liquid crystal material arealigned substantially vertically with respect to surfaces of the firstsubstrate and the second substrate in the state where no voltage isapplied.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga negative refractive index anisotropy at least one of between the firstsubstrate and the polarizer closer to the first substrate than to thesecond substrate and between the second substrate and the polarizercloser to the second substrate than to the first substrate.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one monoaxial phase plate havinga positive refractive index anisotropy at least one of between the firstsubstrate and the polarizer closer to the first substrate than to thesecond substrate and between the second substrate and the polarizercloser to the second substrate than to the first substrate.

In one embodiment of the invention, the liquid crystal display devicefurther includes a pair of polarizers interposing the first substrateand the second substrate, and at least one biaxial phase plate at leastone of between the first substrate and the polarizer closer to the firstsubstrate than to the second substrate and between the second substrateand the polarizer closer to the second substrate than to the firstsubstrate.

In one embodiment of the invention, the liquid crystal layer includes achiral dopant, and the liquid crystal molecules have a spiral pitchwhich is about four times the thickness of the liquid crystal layer.

According to another aspect of the invention, a method for producing aliquid crystal display device including a first substrate, a secondsubstrate, and a liquid crystal layer interposed between the firstsubstrate and the second substrate and formed of a liquid crystalmaterial having liquid crystal molecules, wherein the first substrateincludes a first electrode facing the liquid crystal layer; the secondsubstrate includes a second electrode facing the liquid crystal layer;the first electrode, the second electrode, and a region of the liquidcrystal layer supplied with a voltage by the first electrode and thesecond electrode define a pixel region which is a unit for display; andthe pixel region includes a plurality of sub pixel regions, in each ofwhich the liquid crystal molecules are aligned in an axial symmetricalmanner includes the steps of forming a plurality of openings regularlyarranged in at least one of the first electrode and the second electrodein the pixel region, so that the at least one of the first electrode andthe second electrode having the openings include a plurality ofpolygonal sub electrode regions, each of which has a part of theopenings at least at one of corners and along and overlapping sidesthereof; injecting a mixture of a photocurable resin and the liquidcrystal material into a gap between the first substrate and the secondsubstrate; and irradiating the mixture with light while supplying themixture with a voltage, thereby curing the photocurable resin and thusforming an alignment fixing layer.

In an LCD device according to the present invention, an electrode forapplying a voltage to the liquid crystal layer has an opening (an areawhich does not act as an electrode) in a pixel region, which is a unitfor display. Since no electric field is generated at the opening, anelectric field around the opening is inclined with respect to adirection normal to the surface of the electrode. For example, liquidcrystal molecules having a negative dielectric anisotropy are aligned sothat longitudinal axes thereof are vertical to the electric field.Accordingly, the liquid crystal molecules are aligned in a radial (i.e.,axially symmetrical) manner around the opening due to the obliqueelectric field. As a result, the dependency of the display quality ofthe LCD device on the viewing angle, which is caused by the refractiveindex anisotropy of the liquid crystal molecules, is averaged in allazimuth directions.

In an embodiment where polygonal sub electrode regions having openingsat least either at corners or along and overlapping sides thereof, theliquid crystal molecules are aligned in an axially symmetrical manner ina plurality of sub pixel regions in each of the pixel regions. In anembodiment where the polygonal sub electrode regions are congruent toeach other, the sub pixel regions defined by the polygonal sub electroderegions are arranged highly symmetrically. Accordingly, the uniformityof the viewing angle characteristic is improved. In an embodiment wherethe polygons each have rotationary symmetry (n-fold symmetry), theviewing characteristic is further improved.

In an embodiment where the electrode has a recessed portion in a pixelregion, the liquid crystal molecules above the recessed portion arealigned vertically with respect to an area of the vertical alignmentlayer, the area being concaved in conformity of the recessed portion. Inother words, the liquid crystal molecules above the recessed portion aretilted in an axially symmetrical manner with respect to the center axisof the recessed portion. In an embodiment where the recessed portion isat an intermediate position between two adjacent openings, the axis forthe axial symmetrical alignment matches the center axis of the recessedportion. Thus, the position of the center axis for the axial symmetricalalignment is secured and stabilized.

In an embodiment where the openings are at least 2 μm away from the edgeof the pixel electrode, the alignment of the liquid crystal molecules isprevented from becoming unstable due to the lateral electric fieldgenerated by scanning lines and signal lines (bus lines) provided forconnecting the active devices in the vicinity of an edge of the pixelelectrode.

In an embodiment where at least one side of at least one sub electroderegion matches at least one edge of the pixel electrode, generation ofdisclination at the edge of the pixel electrode is suppressed.

In an embodiment where an alignment fixing layer is provided between theliquid crystal layer and at least either the first substrate or thesecond substrate, the alignment of the liquid crystal molecules isstabilized, which provides a bright display.

Thus, the invention described herein makes possible the advantages ofproviding an LCD device having a satisfactory viewing anglecharacteristic and generating no image sticking phenomenon, and a methodfor producing the same.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of an LCD device in a first exampleaccording to the present invention, illustrating the state when novoltage is applied;

FIG. 1B is a cross-sectional view of the LCD device shown in FIG. 1A,illustrating the state when a voltage is applied;

FIG. 2 is a top view of an active matrix substrate of the LCD deviceshown in FIG. 1A;

FIG. 3 is a view of the LCD device shown in FIG. 1A observed with apolarizing microscope in a crossed nicols state, the LCD device beingsupplied with a voltage for gray scale display;

FIGS. 4A, 4B and 4C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the first example;

FIGS. 5A, 5B and 5C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the first example;

FIG. 6 is a top view of an active matrix substrate of an LCD device in asecond example according to the present invention;

FIG. 7 is a cross-sectional view of the active matrix substrate takenalong line VII-VII′ in FIG. 6;

FIG. 8 is a view of the LCD device in the second example observed with apolarizing microscope in a crossed nicols state, the LCD device beingsupplied with a voltage for gray scale display;

FIGS. 9A, 9B and 9C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the second example;

FIGS. 10A, 10B and 10C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the second example;

FIG. 11 is a top view of an active matrix substrate of an LCD device ina third example according to the present invention;

FIGS. 12A, 12B and 12C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the third example;

FIGS. 13A, 13B and 13C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the third example;

FIG. 14A is a cross-sectional view of an LCD device in a fourth exampleaccording to the present invention, illustrating the state when novoltage is applied;

FIG. 14B is a cross-sectional view of the LCD device shown in FIG. 14A,illustrating the state when a voltage is applied;

FIG. 15 is a top view of an active matrix substrate of the LCD deviceshown in FIG. 14A;

FIG. 16 is a view of the LCD device shown in FIG. 14A observed with apolarizing microscope in a crossed nicols state, the LCD device beingsupplied with a voltage for gray scale display;

FIGS. 17A, 17B and 17C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the fourth example;

FIGS. 18A, 18B and 18C are top views of active matrix substrates,illustrating various alternative arrangements of openings of the pixelelectrode in the fourth example;

FIG. 19A is a cross-sectional view of an LCD device in a fifth exampleaccording to the present invention, illustrating the state when novoltage is applied;

FIG. 19B is a cross-sectional view of the LCD device shown in FIG. 19A,illustrating the state when a voltage is applied;

FIGS. 20A and 20B are each a view of an LCD device observed with apolarizing microscope in a crossed nicols state, illustrating theaxially symmetrical alignment of the liquid crystal molecules disturbedby plastic beads;

FIGS. 21A, 21B, 21C and 21D are each a top view of an active matrixsubstrate in a sixth example according to the present invention, eachsubstrate including a column-like projection;

FIGS. 22A and 22B are each a view of an LCD device in the sixth exampleobserved with a polarizing microscope in a crossed nicols state, the LCDdevice being supplied with a voltage for gray scale display;

FIGS. 23A and 23B are each a view of an LCD device in a seventh exampleaccording to the present invention observed with a polarizing microscopein a crossed nicols state, the LCD device being supplied with a voltagefor gray scale display;

FIGS. 24A and 24B are each a cross-sectional view of an LCD device in aneighth example according to the present invention, including a phaseplate or phase plates;

FIG. 25A is a graph illustrating the dependency of the lighttransmittance on the viewing angle of LCD devices including LCD devicesshown in FIG. 24B in a black display state;

FIG. 25B is a graph illustrating the relationship between the lighttransmittance and the retardation of the phase plate when the viewingangle is 60 degrees;

FIGS. 26A and 26B are each a cross-sectional view of an LCD device inthe eighth example, including a phase plate or phase plates;

FIG. 27A is a graph illustrating the dependency of the lighttransmittance on the viewing angle of LCD devices including LCD devicesshown in FIG. 26B in a black display state;

FIG. 27B is a graph illustrating the relationship between the lighttransmittance and the retardation of the phase plate when the viewingangle is 60 degrees; and

FIGS. 28A, 28B and 28C are each across-sectional view of an LCD devicein the eighth example, including a phase plate or phase plates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings. Inthe following examples, transmission LCD devices will be described, butthe present invention is not limited to this type of LCD devices.

EXAMPLE 1

A LCD device 100 in a first example according to the present inventionwill be described. FIGS. 1A and 1B are schematic cross-sectional viewsof the LCD device 100. FIG. 1A shows the state when no voltage isapplied, and FIG. 1B shows the state when a voltage is applied. FIGS. 1Aand 1B show one pixel region of the LCD device 100. Unless otherwisespecified, the following description will be given regarding the onepixel region.

The LCD device 100 includes an active matrix substrate 20, a countersubstrate (color filter substrate) 30, and a liquid crystal layer 40interposed between the active matrix substrate 20 and the countersubstrate 30. The active matrix substrate 20 includes a transparent baseplate 21, an insulating layer 22, a pixel electrode 24, and an alignmentlayer 26. The insulating layer 22, the pixel electrode 24, and thealignment layer 26 are sequentially provided in this order on a surface21 a of the base plate 21, the surface 21 a facing the liquid crystallayer 40. The active matrix substrate 20 includes an active device(typically, a TFT) and lines for applying a voltage to the pixelelectrode 24, which are not shown in FIG. 1A or 1B for simplicity. Thecounter substrate 30 includes a transparent base plate 31, a colorfilter layer 32, a counter electrode 34, and an alignment layer 36. Thecolor filter layer 32, the counter electrode 34, and the alignment layer36 are provided in this order on a surface 31 a of the base plate 31,the surface 31 a facing the liquid crystal layer 40. In this example,the alignment layers 26 and 36 are vertical alignment layers, and theliquid crystal layer 40 is formed of a liquid crystal material having anegative dielectric material.

The pixel electrode 24 has a plurality of openings 24 a, which arecircular in this example. Needless to say, the plurality of openings 24a do not act as an electrode. As described later in detail, theplurality of openings 24 a define a polygonal sub electrode region 50having the openings 24 a at corners or along and overlapping sidesthereof. The liquid crystal molecules 40 a in a sub pixel region 60defined by the sub electrode region 50 are aligned in an axiallysymmetrical manner by the action of the openings 24 a.

When no voltage is applied to the liquid crystal layer 40 as shown inFIG. 1A, the liquid crystal molecules 40 a are aligned vertically tosurfaces 26 a and 36 a of the vertical alignment layers 26 and 36 by thealignment force thereof. In this specification, the expression “surfaceof the first substrate” and “surface of the second substrate” refer tothe direction parallel to the surface 26 a. When a voltage is applied tothe liquid crystal layer 40 as shown in FIG. 1B, the liquid crystalmolecules 40 a, which have a negative dielectric anisotropy, are alignedso that longitudinal axes thereof are vertical with respect to anelectric line of force E. In the vicinity of the openings 24 a, theelectric line of force E is inclined with respect to the surfaces 21 aand 31 a of the base plates 21 and 31 (substantially parallel to thesurfaces 26 a and 36 a of the vertical alignment layers 26 and 36).Accordingly, the liquid crystal molecules 40 a in the vicinity of theopenings 24 a are aligned radially around each opening 24 a. The liquidcrystal molecules 40 a farther from the opening 24 a are tilted at agreater angle with respect to the line normal to the surfaces 21 a and31 a than the liquid crystal molecules 40 a closer to the opening 24 a.Thus, the liquid crystal molecules 40 a in the sub pixel region 60 arealigned in an axially symmetrical manner.

FIG. 2 is a top view of the active matrix substrate 20 of the pixelregion of the LCD device 100 shown in FIGS. 1A and 1B. FIGS. 1A and 1Billustrate the cross-section taken along line I-I′ in FIG. 2.

As shown in FIG. 2, the active matrix substrate 20 includes a TFT 70 forcontrolling the voltage to be applied to the pixel electrode 24, a gateline (scanning line) 72 for supplying a scanning signal to a gateelectrode of the TFT 70, a source line (signal line) 74 for supplying adata signal to a source electrode of the TFT 70, and a storagecapacitance common line 76 having the same potential as that of thepixel electrode 24. In this example, a so-called Cs-on-Common structurein which a storage capacitance is formed using the storage capacitancecommon line 76 is used. Alternatively, a so-called Cs-on-Gate structurein which a storage capacitance is formed using the gate line 72 isusable, or formation of the storage capacitance can be omitted.

As described above, the pixel electrode 24 has the plurality of openings24 a. The openings 24 a will be described in detail with reference toFIG. 2. As shown in FIG. 2, the openings 24 a define sub electroderegions 50 a, 50 b and 50 c (each corresponding to the sub electroderegion 50 in FIGS. 1A and 1B). The sub electrode regions 50 a, 50 b and50 c have the openings 24 a at corners thereof. In more detail, the subelectrode regions 50 a, 50 b and 50 c are polygons defined by lineslinking centers of each two openings 24 a which are closest to eachother. In this example, the sub electrode regions 50 a, 50 b and 50 care quadrangular. A cut-off part of the pixel electrode 24 a (lower leftpart in FIG. 2) in the vicinity of the sub electrode region 50 c formsan opening. The sub electrode regions 50 a and 50 c are squares, havinga four-fold axis of symmetry at centers thereof, which are congruent toeach other. The sub electrode region 50 b is a rectangle having atwo-fold axis of symmetry at a center thereof. The sub electrode region50 b shares one side with each of the sub electrode regions 50 a and 50c.

The LCD device 100 in the first example can be produced in, for example,the following manner (refer to FIGS. 1A and 1B regarding the referencenumerals). The active matrix substrate 20 can be produced by a knownmethod used for producing an active matrix substrate, except that thepixel electrode 24 is formed by using a pattern which causes theopenings 24 a as shown in FIG. 2 to be formed. Thus, the active matrixsubstrate 20 can be produced without increasing the number of productionsteps. The counter substrate 30 can also be produced by a known method.The pixel electrode 24 and the counter electrode 34 are formed of, forexample, ITO (indium tin oxide) to have a thickness of about 50 nm.

The laminate including the base plate 21, the insulating layer 22, andthe pixel electrode 24 is coated with the vertical alignment layer 26 byprinting. The laminate including the base plate 31, the color filterlayer 32, and the counter electrode 34 is coated with the verticalalignment layer 36 by printing. The vertical alignment layers 26 and 36are formed of a polyimide-based material (for example, JALS-204, JapanSynthetic Rubber Co., Ltd.). Alternatively, the vertical alignmentlayers 26 and 36 can be formed of various other materials which causeliquid crystal molecules to be aligned vertically with respect to thesurfaces 26 a and 36 a of the vertical alignment layers 26 and 36. Suchmaterials include, for example, octadecyl ethoxysilane and lecithin.Thus, the active matrix substrate 20 and the counter substrate 30 areformed.

Then, plastic beads having a diameter of about 4.5 μm are distributed onthe vertical alignment layer 26. On the counter substrate 30, a sealsection formed of an epoxy resin including fiberglass is formed along aperiphery of a display area by screen printing. The active matrixsubstrate 20 and the counter substrate 30 are bonded together and curedby heating. Next, a liquid crystal material having a negative dielectricanisotropy (Δ∈4.0, Δn=0.08) is injected into a gap between the activematrix substrate 20 and the counter substrate 30 using vacuum injection.In this manner, the LCD device 100 is completed.

In this example, the pixel electrode 24 has openings 24 a.Alternatively, the counter electrode 34 can have openings. The effect ofthe present invention is obtained by forming a plurality of openings inan electrode provided in a pixel region, which is a unit for display.Forming the openings 24 a in the pixel electrode 24 is advantageous inthat the openings 24 a are formed in the step of forming the pixelelectrode 24 by patterning a conductive film and thus the number ofproduction steps is not increased.

FIG. 3 shows a top view of one pixel region (represented as 10 a in FIG.3) of the LCD device 100 shown in FIG. 2 which is observed with apolarizing microscope in a crossed nicols state. In FIG. 3, the LCDdevice 100 is supplied with a voltage for gray scale display. The pixelregion 100 a includes sub pixel regions 60 a, 60 b and 60 c which arerespectively defined by the sub electrode regions 50 a, 50 b and 50 c inFIG. 2. A part of the pixel region 10 a corresponding to the TFT 70, thegate line 72, the source line 74 (FIG. 2) and the like which block light(or a part corresponding to a black matrix) is observed to be black(hatched in FIG. 3). The openings 24 a are also observed to be black.The storage capacitance common line 76 is formed of a transparentmaterial. In this example, the pixel region pitch in the longer side isabout 300 μm, the pixel region pitch in the shorter side is about 100μm, and the diameter of each opening 24 a is about 10 μm.

As can be appreciated from FIG. 3, the sub pixel regions 60 a, 60 b and60 c are observed to have a crossed extinction pattern, whichdemonstrates that the liquid crystal molecules are aligned in an axiallysymmetrical manner. In the sub pixel regions 60 a and 60 c which aresquare, an extinction pattern having a four-fold axis of symmetry isobserved. In the sub pixel region 60 b which is rectangular, anextinction pattern having a two-fold axis of symmetry is observed. In aperipheral region 60 d surrounding the sub pixel regions 60 a, 60 b and60 c, an extinction pattern which is similar to that in each of the subpixel regions is observed. Such a phenomenon demonstrates that theliquid crystal molecules are aligned in an axially symmetrical manner inthe peripheral region 60 d. In other words, in the peripheral region 60d, the liquid crystal molecules are aligned substantially radiallyaround each opening 24 a. This occurs since the alignment of the liquidcrystal molecules 40 a tilted by the oblique electric field generated bythe opening 24 a is conveyed to the liquid crystal molecules in theperipheral region 60 d.

In such an LCD device 100, each of a plurality of pixel regions, in itsentirety, has sub regions in which the liquid crystal molecules 40 a(FIGS. 1A and 1B) are aligned in an axially symmetrical manner.Accordingly, the viewing angle characteristic of the LCD device 100 doesnot vary in accordance with the azimuth angle of the viewing direction,and thus the LCD device 100 has a high viewing angle characteristic.When no voltage is applied to the liquid crystal layer 40 (FIGS. 1A and1B), substantially all the liquid crystal molecules are vertical withrespect to the surfaces 21 a and 31 a of the glass plates 21 and 31, andthus a satisfactory black display is provided. When a voltage isapplied, satisfactory white display is provided with a response time ofabout 20 msec. When a voltage for gray scale display is applied, theaxially symmetrical alignment of the liquid crystal molecules is notdisturbed. The response time is sufficiently short, and no imagesticking phenomenon is exhibited. The axially symmetrical alignment isquite stable, and no defective alignment is generated in a repeatedoperation test.

In this example, the sub electrode regions 50 a, 50 b and 50 c arequadrangular. The sub electrode regions do not need to be quadrangular,but can be a polygon having openings at corners or along and overlappingsides thereof. The sub electrode regions can be a triangle, butpreferably is a polygon having four or more corners in order to providea uniform dependency on the azimuth angle of the viewing characteristic.A square is more advantageous than a rectangle since a square has higherrotationary symmetry and thus provides a more uniform viewingcharacteristic than a rectangle.

FIGS. 4A, 4B and 4C show different alternative arrangements of the subelectrode regions 50 of the pixel electrode 24 in the first example. InFIGS. 4A, 4B and 4C, the sub electrode regions 50 are quadrangular.FIGS. 5A, 5B and 5C show still different alternative arrangements of thesub electrode regions of the pixel electrode 24 in the first example.FIGS. 5A, 5B and 5C, the sub electrode regions are polygons having fiveor more corners.

In FIG. 5A, hexagonal sub electrode regions 51 each have the openings 24a at corners thereof. In FIG. 5B, hexagonal regions each have theopenings 24 a at corners and at a center thereof, so that the liquidcrystal molecules are aligned in an axially symmetrical manner intriangular sub electrode regions 52. In FIG. 5C, octagonal sub electroderegions 53 each have openings 24 c, which are rectangular, along sidesthereof. The openings 24 a do not need to be circular or rectangular,but can be of any shape. The sub electrode regions (and also sub pixelregions), which preferably have high rotationary symmetry (i.e., asclose as possible to a circle), are preferably equilateral polygons. Theplurality of sub electrode regions (and also the sub pixel regions) arepreferably arranged to have rotationary symmetry. Accordingly, it ispreferable to arrange congruent equilateral polygons in a regularmanner.

The sub electrode regions (and also the sub pixel regions) each can havea side of about 20 μm to about 50 μm in order to align the liquidcrystal molecules in an axial symmetrical manner stably. The openings 24a, when being circular, preferably have a diameter of about 5 μm toabout 20 μm. When the number of openings is excessive, the numericalaperture of the LCD device 100 is reduced. The number and arrangement(shape of the sub electrode and pixel regions) of the openings 24 a needto be appropriately determined in consideration of both the viewingangle and brightness required by the use of the LCD device 100.

EXAMPLE 2

An LCD device in a second example according to the present inventionwill be described with reference to FIGS. 6 and 7. In this example, thepixel electrode has openings and also a recessed portion as described indetail later. FIG. 6 is a top view of an active matrix substrate 80 ofthe LCD device in the second example. FIG. 6 shows one pixel region ofthe LCD device. Unless otherwise specified, the following descriptionwill be given regarding one pixel region.

As shown in FIG. 6, the active matrix substrate 80 includes a pixelelectrode 24. The pixel electrode 24 has openings 24 a and a recessedportion 24 b. Except for the recessed portion 24 b, the structure of theLCD device in the second example is substantially identical with that ofthe LCD device 100 in the first example. Identical elements previouslydiscussed with respect to FIGS. 1A, 1B, 2 and 3 bear identical referencenumerals and the descriptions thereof will be omitted. The recessedportion 24 b can be formed in the counter electrode in lieu of the pixelelectrode 24.

FIG. 7 is a cross-sectional view of the active matrix substrate 80 takenalong line VII-VII′ in FIG. 6. The insulating layer 22 provided on thebase plate 21 has a recessed portion. The pixel electrode 24 provided onthe insulating layer 22 also has a recessed portion 24 b accordingly.The recessed portion 24 b has a depth of, for example, about 5 μm and adiameter of, for example, about 10 μm. The openings 24 a formed in thepixel electrode 24 has a diameter of, for example, about 10 μm. Thevertical alignment layer 26 is provided on the pixel electrode 24.

When no voltage is applied, the liquid crystal molecules 40 a above therecessed portion 24 b are aligned vertically with respect to the surface26 a of the vertical alignment layer 26. When a voltage is applied, theliquid crystal molecules 40 a above the recessed portion 24 b are tiltedto be aligned in an axial symmetrical manner with respect to a centralaxis 40 b of the recessed portion 24 b represented by the dashed line inFIG. 7. As shown in FIG. 7, the direction of the tilt with respect tothe central axis 40 b is opposite to the direction of tilt of the liquidcrystal molecules 40 a caused by the oblique electric field around theopening 24 a. More specifically, in the vicinity of the recessed portion24 b, each of the liquid crystal molecules 40 a is tilted so that oneend, closer to the center axis 40 b of the recessed portion 24 b, ishigher (i.e., farther from the pixel electrode 24) than the other end,farther from the center axis 40 b of the recessed portion 24 b. Bycontrast, in the vicinity of the opening 24 a, each of the liquidcrystal molecules 40 a is tilted so that one end, closer to the centeraxis 40 c of the opening 24 a, is lower (i.e., closer to the pixelelectrode 24) than the other end, farther from the center axis 40 c ofthe opening 24 a. Accordingly, the recessed portion 24 b, formed at anintermediate position between two adjacent openings 24 a, stabilizes theaxial symmetrical alignment of the liquid crystal molecules 40 a aroundthe openings 24 a. In other words, the liquid crystal molecules 40 a inthe sub pixel region 60 are stably aligned in an axially symmetricalmanner around the central axis 40 b of the recessed portion 24 b.

Returning to FIG. 6, recessed portions 24 b are also formed atsymmetrical positions in a peripheral region 50 d around the subelectrode regions 50 a, 50 b and 50 c. Thus, the axially symmetricalalignment of the liquid crystal molecules 40 a in a peripheral regionaround the sub pixel regions are stabilized to secure the position ofthe axis of symmetry.

As can be appreciated from the above description, the recessed portions24 b and the openings 24 a define sub pixel regions together.Accordingly, the recessed portions 24 b are preferably located so as toform polygons congruent to the polygons formed by the openings 24 a. Therecessed portion 24 b can have any shape in lieu of a circle.

The LCD device in the second example can be produced in a similar mannerto that described in the first example. The insulating layer 22 havingthe recessed portion is formed by, for example, forming a silicon oxidefilm having a thickness of about 10 μm by sputtering or the like andthen performing etching using a mask having an opening corresponding tothe recessed portion. Accordingly, the pixel electrode 24 formed on theinsulating layer 22 has the recessed portion 24 b. The shape, size anddepth of the recessed portion 24 b are adjusted by the shape and size ofthe opening of the mask, the thickness of the insulating layer 22, andthe etching amount. The recessed portion 24 b preferably has a diameterof about 5 μm through about 20 μm like the opening 24 a.

FIG. 8 shows a top view of one pixel region (represented as 100 b inFIG. 8) of the LCD device in the second example which is observed with apolarizing microscope in a crossed nicols state. In FIG. 8, the LCDdevice is supplied with a voltage for gray scale display. The pixelregion 100 b includes sub pixel regions 60 a, 60 b and 60 a which arerespectively defined by the sub electrode regions 50 a, 50 b and 50 c inFIG. 6. A part of the pixel region 100 b corresponding to the TFT 70,the gate line 72, the source line 74 (FIG. 2) and the like which blocklight (or a part corresponding to a black matrix) is observed to beblack (hatched in FIG. 8). The openings 24 a are also observed to beblack. The storage capacitance common line 76 is formed of a metalmaterial. In this example, the pixel region pitch in the longer side isabout 300 μm, the pixel region pitch in the shorter side is about 100μm, and the diameter of each opening 24 a is about 10 μm.

In such an LCD device, each of a plurality of pixel regions, in itsentirety, has sub regions in which the liquid crystal molecules 40 a(FIG. 7) are aligned in an axially symmetrical manner. The axis ofsymmetry is controlled and secured by the recessed portions 24 b (FIG.6). The axis of symmetry also matches the recessed portions 24 b.Accordingly, the LCD device has a high viewing angle characteristic. Theresponse time is sufficiently short, and no image sticking phenomenon isexhibited. The axially symmetrical alignment is quite stable, and nodefective alignment is generated in a repeated operation test.

In this example, the sub electrode regions 50 a, 50 b and 50 c arequadrangular. The sub electrode regions do not need to be quadrangular.In combination with the openings 24 a shown in FIGS. 4A, 4B, 4C, therecessed portions 24 b shown in FIGS. 9A, 9B and 9C can be formed, Arespectively. In combination with the openings 24 a shown in FIGS. 5A,5B, 5C, the recessed portions 24 b shown in FIGS. 10A, 10B and 10C canbe formed, respectively. The recessed portions 24 b act to secure andstabilize the center for axial symmetry. Therefore, the recessedportions 24 b are each preferably formed at an intermediate positionbetween two adjacent openings 24 a. Furthermore, the recessed portions24 b are preferably formed so as to form polygons congruent to thepolygons formed by the openings 24 a. The recessed portions 24 b in aperipheral region 50 d (FIG. 6) are preferably located so as to formpolygons congruent to the polygons formed by the recessed portions 24 bin the sub electrode region 50.

When the recessed portions 24 b are formed, the sub pixel region 60 canhave a side of about 50 μm to about 100 μm in order to stabilize theaxially symmetrical alignment of the liquid crystal molecules. The shapeand number of the recessed portions 24 b can be appropriately determinedin consideration of both the viewing angle and brightness required bythe use of the LCD device.

EXAMPLE 3

An LCD device in a third example according to the present invention willbe described. FIG. 11 is a top view of an active matrix substrate 320 ofthe LCD device in the third example. FIG. 11 shows one pixel region ofthe LCD device. Unless otherwise specified, the following descriptionwill be given regarding one pixel region. In the active matrix substrate320, distance d from an edge 24 a of the pixel electrode 24 to anopening 324 a, which is closest to the edge 24 c, and distance d′ froman edge 24 d to the opening 324 a (also closest to the edge 24 d) areboth about 5 μm. Except for this point, the LCD device in the thirdexample is substantially identical with the LCD device 100 in the firstexample. Identical elements previously discussed with respect to FIGS.1A, 1B, 2 and 3 bear identical reference numerals and the descriptionsthereof will be omitted.

Distances d and d′ are not limited to about 5 μm, but are preferablyabout 2 μm or more. More preferably, distances d and d′ are about 2 μmto about 10 μm. When distances d and d′ are less than about 2 μm, theaxially symmetrical alignment of the liquid crystal molecules isdisturbed by a lateral (horizontal) electric field due to a scanningline or a signal line (bus line) located in the vicinity of a pluralityof pixel electrodes 24 arranged in a matrix. When distances d and d′ aremore than about 10 μm, an area of the pixel electrode 24 contributing tothe display is excessively reduced, and thus light transmittance of theLCD device is excessively reduced.

The LCD device in the third example can be produced in a similar mannerto that described in the first example.

When one pixel region of the LCD device in the third example suppliedwith a voltage for gray scale display is examined by a polarizingmicroscope in a crossed nicols state, the liquid crystal molecules areobserved to be in a similar state to the state described in the firstexample.

In such an LCD device, each of a plurality of pixel regions, in itsentirety, has sub regions in which the liquid crystal molecules arealigned in an axially symmetrical manner. Accordingly, the LCD devicehas a high viewing angle characteristic. The response time issufficiently short, and no image sticking phenomenon is exhibited. Theaxially symmetrical alignment is quite stable, and no defectivealignment is generated in a repeated operation test.

In this example, the sub electrode regions 50 a, 50 b and 50 a arequadrangular. The sub electrode regions do not need to be quadrangular,but can be a polygon having openings at corners or along and overlappingsides thereof.

FIGS. 12A, 12B and 12C show different alternative arrangements of thesub electrode regions 50 of the pixel electrode 24 in the third example.In FIGS. 12A, 12B and 12C, the sub electrode regions 50 arequadrangular. FIGS. 13A, 13B and 13C show still different alternativearrangements of the sub electrode regions 50 of the pixel electrode 24in the third example.

In FIGS. 13A, 13B and 13C, the sub electrode regions are polygons havingfive or more corners.

In FIG. 13A, hexagonal sub electrode regions 51 each have the openings324 a at corners thereof. In FIG. 13B, hexagonal regions each have theopening 324 a at corners and at a center thereof, so that the liquidcrystal molecules are aligned in an axially symmetrical manner intriangular sub electrode regions 52. In FIG. 13C, octagonal subelectrode regions 53 each have openings 324 a, which are rectangular,along sides thereof. The openings 324 a do not need to be circular orrectangular, but can be of any shape. The sub electrode regions (andalso sub pixel regions), which preferably have high rotationary symmetry(i.e., as close as possible to a circle), are preferably equilateralpolygons. The plurality of sub electrode regions (and also the sub pixelregions) are preferably arranged to have rotationary symmetry.Accordingly, it is preferable to arrange congruent equilateral polygonsin a regular manner.

The sub electrode regions (and also the sub pixel regions) each can havea side of about 20 μm to about 50 μm in order to align the liquidcrystal molecules in an axial symmetrical manner stably. As describedabove, distance d between the edge 24 c and the opening 324 a closest tothe edge 24 c and distance d′ between the edge 24 a and the opening 324a (also closest to the edge 24 d) are each preferably about 2 μm ormore, and more preferably about 2 μm to about 10 μm. The openings 324 a,when being circular, preferably have a diameter of about 5 μm to about20 μm. When the number of openings is excessive, the numerical apertureof the LCD device is reduced. The number and arrangement (shape of thesub electrode and pixel regions) of the openings 324 a need to beappropriately determined in consideration of both the viewing angle andbrightness required by the use of the LCD device.

In the LCD device in the third example, recessed portions regularlyarranged in each pixel region can be formed in at least one of the pixelelectrode or the counter electrode as the LCD device in the secondexample.

EXAMPLE 4

A LCD device 400 in a fourth example according to the present inventionwill be described. FIGS. 14A and 14B are schematic cross-sectional viewsof the LCD device 400. FIG. 14A shows the state when no voltage isapplied, and FIG. 14B shows the state when a voltage is applied. FIGS.14A and 14B show one pixel region of the LCD device 400. Unlessotherwise specified, the following description will be given regardingone pixel region. As shown in FIGS. 14A and 14B, the LCD device 400includes an active matrix substrate 420, a counter substrate 30, and aliquid crystal layer 40 interposed therebetween.

In the LCD device 400, openings 424 a, which are circular in thisexample, are formed in the pixel electrode 24 (e.g., the lower rightcorner of the sub electrode region 50 a in FIG. 15) and also along andoverlapping edges or at corners of the pixel electrode 24 (e.g., thelower left corner, upper left corner and upper right corner of the subelectrode region 50 a). Except for this point, the LCD device 400 has asubstantially identical structure with that of the LCD device 100.Identical elements previously discussed with respect to FIGS. 1A, 1B, 2and 3 bear identical reference numerals and the descriptions thereofwill be omitted.

When no voltage is applied to the liquid crystal layer 40 as shown inFIG. 14A, the liquid crystal molecules 40 a are aligned vertically tosurfaces 26 a and 36 a of the vertical alignment layers 26 and 36 by thealignment force thereof. When a voltage is applied to the liquid crystallayer 40 as shown in FIG. 14B, the liquid crystal molecules 40 a, whichhave a negative dielectric anisotropy, are aligned so that longitudinalaxes thereof are vertical with respect to an electric line of force E.In the vicinity of the openings 424 a, the electric line of force E isinclined with respect to the surfaces 21 a and 31 a of the base plates21 and 31 (substantially parallel to the surfaces 26 a and 36 a of thevertical alignment layers 26 and 36). Accordingly, the liquid crystalmolecules 40 a in the vicinity of the openings 424 a are alignedradially around each opening 424 a. The liquid crystal molecules 40 afarther from the opening 424 a are tilted at a greater angle withrespect to the line normal to the surfaces 21 a and 31 a than the liquidcrystal molecules 40 a closer to the opening 424 a. Thus, the liquidcrystal molecules 40 a in the sub pixel region 60 are aligned in anaxially symmetrical manner.

FIG. 15 is a top view of the active matrix substrate 420 of the pixelregion of the LCD device 400 shown in FIGS. 14A and 14B. FIGS. 14A and14B illustrate the cross-section taken along lines XIV-XIV′ in FIG. 15.

As described above, the pixel electrode 24 has the plurality of openings424 a. The openings 424 a will be described in detail with reference toFIG. 15. As shown in FIG. 15, the openings 424 a are formed in the pixelelectrode 24 (e.g., the lower right corner of the sub electrode region50 a in FIG. 15) and also along and overlapping edges or at corners ofthe pixel electrode 24 (e.g., the lower left corner, upper left cornerand upper right corner of the sub electrode region 50 a). The openings424 a define sub electrode regions 50 a through 50 i (nine regions inthis example). The sub electrode regions 50 a through 50i have theopenings 424 a at corners thereof. The sub electrode regions 50 a, 50 b,50 c and 50 d are square having a four-fold axis of symmetry) at acenter thereof and are congruent to one another. The sub electroderegions 50 e and 50 f are rectangular (having a two-fold axis ofsymmetry) at a center thereof. The sub electrode region 50 e shares oneside with each of the sub electrode regions 50 c, 50 f and 50 g. The subelectrode region 50 f shares one side with each of the sub electroderegions 50 d, 50 e and 50 h.

In FIG. 15, four edges of the pixel electrode 24 match one side of eachof the sub electrode regions 50 a through 50 i. Such an arrangementsubstantially prevents disclination, which is caused near the edges ofthe pixel electrode by a distance between a side of the sub electroderegion and an edge of the pixel electrode. The reason f or this is that,as shown in FIG. 14B, the direction of tilt of the liquid crystalmolecules 40 a continuously changes in the direction of arrow A (i.e.,from the center to the edge of the pixel electrode 24).

The LCD device 400 in th e fourth example can be produced in a similarmanner to that in the first example.

FIG. 16 shows a top view of one pixel region (represented as 400 a inFIG. 16) of the LCD device 400 shown in FIG. 15 which is observed with apolarizing microscope in a crossed nicols state. In FIG. 16, the LCDdevice 400 is supplied with a voltage for gray scale display. The pixelregion 400 a includes sub pixel regions 60 a through 60 i which arerespectively defined by the sub electrode regions 50 a through 50 i inFIG. 15. A part of the pixel region 400 a corresponding to the TFT 70,the gate line 72, the source line 74 (FIG. 15) and the like which blocklight (or a part corresponding to a black matrix) is observed to beblack (hatched in FIG. 16). The openings 424 a are also observed to beblack. The storage capacitance common line 76 is formed of a transparentmaterial. In this example, the pixel region pitch in the longer side isabout 300 μm, the pixel region pitch in the shorter side is about 100μm, and the diameter of each opening 424 a is about 10 μm.

As can be appreciated from FIG. 16, the sub pixel regions 60 a through60 i are observed to have a crossed extinction pattern, whichdemonstrates that the liquid crystal molecules are aligned in an axiallysymmetrical manner. In the sub pixel regions 60 a through 60 d definedby the square sub electrode regions 50 a through 50 d (FIG. 15), anextinction pattern having a four-fold axis of symmetry is observed. Inthe sub pixel regions 60 e and 60 f defined by the rectangular subelectrode regions 50 e and 50 f (FIG. 15), an extinction pattern havinga two-fold axis of symmetry is observed.

In such an LCD device 400, each of a plurality of pixel regions, in itsentirety, has sub regions in which the liquid crystal molecules 40 a(FIGS. 14A and 14B) are aligned in an axially symmetrical manner.Accordingly, the LCD device 400 has a high viewing angle characteristic.The response time is sufficiently short, and no image stickingphenomenon is exhibited. The axially symmetrical alignment is quitestable, and no defective alignment is generated in a repeated operationtest.

In this example, the sub electrode regions 50 a through 50 i arequadrangular. The sub electrode regions do not need to be quadrangular,but can be a polygon having openings at corners or along and overlappingsides thereof. The sub electrode regions can be a triangle, butpreferably is a polygon having four or more corners in order to providea uniform dependency on the azimuth angle of the viewing characteristic.A square is more advantageous than a rectangle since a square has higherrotationary symmetry and thus provides a more uniform viewingcharacteristic than a rectangle.

FIGS. 17A, 17B and 17C show different alternative arrangements of thesub electrode regions 50 of the pixel electrode 24 in the fourthexample. In FIGS. 17A, 17B and 17C, the sub electrode regions 50 arequadrangular. FIGS. 18A, 18B and 18C show still different alternativearrangements of the sub electrode regions of the pixel electrode 24 inthe fourth example. In FIGS. 18A, 18B and 18C, the sub electrode regionsare polygons having five or more corners.

In FIG. 18A, hexagonal sub electrode regions 51 each have the openings424 a at corners thereof. In FIG. 18B, hexagonal regions each have theopenings 424 a at corners and at a center thereof, so that the liquidcrystal molecules are aligned in an axially symmetrical manner intriangular sub electrode regions 52. In FIG. 18C, octagonal subelectrode regions 53 each have openings 424 a, which are rectangular,along sides thereof. The openings 424 a do not need to be circular orrectangular, but can be of any shape. The sub electrode regions (andalso sub pixel regions), which preferably-have high rotationary symmetry(i.e., as close as possible to a circle), are preferably equilateralpolygons. The plurality of sub electrode regions (and also the sub pixelregions) are preferably arranged to have rotationary symmetry.Accordingly, it is preferable to arrange congruent equilateral polygonsin a regular manner. In either case, the effect of this example can beobtained where at least one side of at least one sub electrode regionmatches at least one of the edges of pixel electrode 24.

In the LCD device 400 in the fourth example, recessed portions regularlyarranged in each pixel region can be formed in at least one of the pixelelectrode 24 or the counter electrode 34 as the LCD device 400 in thesecond example.

In the LCD device in the third example, the openings in the pixelelectrode are distanced from the edges of the pixel electrode. In theLCD device 400 in the fourth example, a side of the sub electrode regionmatches an edge of the pixel electrode. The arrangement of the openingswith respect to the edges of the pixel electrode can be appropriatelyselected in accordance with the use of the LCD device.

EXAMPLE 5

An LCD device 500 in a fifth example according to the present inventionincludes an alignment fixing layer in at least one of first and secondsubstrates in contact with the liquid crystal layer 40 as described indetail below.

FIGS. 19A and 19B are schematic cross-sectional views of the LCD device500. FIG. 19A shows the state when no voltage is applied, and FIG. 19Bshows the state when a voltage is applied. FIGS. 19A and 19B show onepixel region of the LCD device 500. Unless otherwise specified, thefollowing description will be given regarding one pixel region.

The LCD device 500 includes an active matrix substrate 520, a countersubstrate (color filter substrate) 530, and a liquid crystal layer 40interposed between the active matrix substrate 520 and the countersubstrate 530. The active matrix substrate 520 includes a transparentbase plate 21, an insulating layer 22, a pixel electrode 24, analignment layer 26, and an alignment fixing layer 41 a. The insulatinglayer 22, the pixel electrode 24, the alignment layer 26, and thealignment fixing layer 41 a are sequentially provided in this order on asurface 21 a of the base plate 21, the surface 21 a facing the liquidcrystal layer 40. The counter substrate 530 includes a transparent baseplate 31, a color filter layer 32, a counter electrode 34, an alignmentlayer 36, and an alignment fixing layer 41 b. The color filter layer 32,the counter electrode 34, the alignment layer 36, and the alignmentfixing layer 41 b are provided in this order on a surface 31 a of thebase plate 31, the surface 31 a facing the liquid crystal layer 40.Except for the alignment fixing layers 41 a and 41 b, the LCD device 500has a substantially identical structure as that of the LCD device 100.Identical elements previously discussed with respect to FIGS. 1A, 1B, 2and 3 bear identical reference numerals and the descriptions thereofwill be omitted.

The pixel electrode 24 has a plurality of openings 24 a, for example, asshown in FIG. 2. The plurality of openings 24 a defines a polygonal subelectrode region 50 having the openings 24 a at corners or along andoverlapping sides thereof. The liquid crystal molecules 40 a in a subpixel region 60 defined by a sub electrode region 50 are aligned in anaxially symmetrical manner by the action of the openings 24 a. Theopenings 24 a can be arranged as shown in FIGS. 4A through 4C, 5Athrough 5C, 11, 12A through 12C, 13A through 13C, 15, 17A through 17C,and 18A through 18C.

When no voltage is applied to the liquid crystal layer 40 as shown inFIG. 19A, the liquid crystal molecules 40 a are aligned vertically tosurfaces 26 a and 36 a of the vertical alignment layers 26 and 36 by thealignment force thereof. When a voltage is applied to the liquid crystallayer 40 as shown in FIG. 19B, the liquid crystal molecules 40 a, whichhave a negative dielectric anisotropy, are aligned so that longitudinalaxes thereof are vertical with respect to an electric line of force E.In the vicinity of the openings 24 a, the electric line of force B isinclined with respect to the surfaces 21 a and 31 a of the base plates21 and 31 (substantially parallel to the surfaces 26 a and 36 a of thevertical alignment layers 26 and 36). Accordingly, the liquid crystalmolecules 40 a in the vicinity of the openings 24 a are aligned radiallyaround each opening 24 a. The liquid crystal molecules 40 a farther fromthe opening 24 a are tilted at a greater angle with respect to the linenormal to the surfaces 21 a and 31 a than the liquid crystal molecules40 a closer to the opening 24 a. Thus, the liquid crystal molecules 40 ain the sub pixel region 60 are aligned in an axially symmetrical manner.The alignment fixing layers 41 a and 41 b uniformly and stably maintainpretilt of the axial symmetrical alignment of the liquid crystalmolecules in the sub pixel region 60 caused when a voltage is applied tothe LCD device 500. The alignment fixing layers 41 a and 41 b alsomaintain the pretilt when no voltage is applied. The alignment fixinglayers 41 a and 41 b maintain the axially symmetrical alignment evenafter the power is turned off.

The LCD device 500 in the fifth example can be produced in, for example,the following manner. The active matrix substrate 520 can be produced bya known method used for producing an active matrix substrate, exceptthat the pixel electrode 24 is formed by using a pattern which causesthe openings 24 a as shown in FIG. 2 to be formed. Thus, the activematrix substrate 520 can be produced without increasing the number ofproduction steps. The counter substrate 30 can also be produced by aknown method. The pixel electrode 24 and the counter electrode 34 areformed of, for example, ITO (indium tin oxide) to have a thickness ofabout 50 nm.

The laminate including the base plate 21, the insulating layer 22 andthe pixel electrode 24 is coated with the vertical alignment layer 26 byprinting. The laminate including the base plate 31, the color filterlayer 32 and the counter electrode 34 is coated with the verticalalignment layer 36 by printing. The vertical alignment layers 26 and 36are formed of a polyimide-based material (for example, JALS-204, JapanSynthetic Rubber Co., Ltd.). Alternatively, the vertical alignmentlayers 26 and 36 can be formed of various other materials which causeliquid crystal molecules to be aligned vertically with respect to thesurfaces 26 a and 36 a of the vertical alignment layers 26 and 36. Suchmaterials include, for example, octadecyl ethoxysilane and lecithin.

Then, plastic beads having a diameter of about 4.5 μm are distributed onthe vertical alignment layer 26. On the vertical alignment layer 36, aseal section formed of an epoxy resin including fiber glass is formedalong a periphery of a display area by screen printing. The resultantlaminates are bonded together and cured by heating. Next, a mixture of aliquid crystal material, a photocurable resin (0.3% by weight), and aphotoinitiator (0.1% by weight) is injected into a gap between theactive matrix substrate 520 and the counter substrate 530 using vacuuminjection, thereby forming the liquid crystal layer 40. The liquidcrystal material has a negative dielectric anisotropy (Δ∈=−4.0,Δn=0.08). The photocurable resin can be represented by the followingchemical formula. The photoinitiator can be, for example, Irgacure 651(Ciba-Geigy Corporation).

When a voltage of, for example, about 5 V is applied between the pixelelectrode 24 and the counter electrode 34, the liquid crystal molecules40 a, which have been vertically aligned to the surfaces 26 a and 36 aof the vertical alignment layers 26 and 36, are tilted toward adirection parallel to the surfaces 26 a and 36 a (i.e., vertical to theelectric field). Thus, the liquid crystal molecules 40 a are aligned inan axially symmetrical manner with respect to the center axis of eachopening 24 a.

When the liquid crystal layer 40 is irradiated with ultraviolet rays (6mW/cm², 365 nm) for about 10 minutes at room temperature (25° C.) whileapplying a voltage of about 2.2 V, which is about 0.3 V higher than athreshold voltage, between the pixel electrode 24 and the counterelectrode 34, the photocurable resin in the mixture is cured. Thus, thealignment fixing layers 41 a and 41 b are formed. Thus, the LCD device500 is completed. The threshold voltage is a voltage at which the lighttransmittance is 10% in the voltage-light transmittance curve of an LCDdevice.

The alignment fixing layers 41 a and 41 b define the pretilt andalignment direction of the axially symmetrical alignment. The voltageapplied during the ultraviolet irradiation is preferably about 0.2 V toabout 0.5 V higher, and more preferably about 0.3 V to about 0.4 Vhigher than the threshold voltage. When the voltage is excessively lowwith respect to the threshold voltage, the alignment force generated bythe alignment fixing layers 41 a and 41 b is not sufficiently large.When the voltage is excessively high, the alignment is excessivelyfixed, thus causing an image sticking phenomenon or the like. By formingthe alignment fixing layers 41 a and 41 b while applying an appropriatevoltage, the axially symmetrical alignment of the liquid crystalmolecules 40 a can be rapidly reproduced.

Such a structure does not require projections to be provided in theliquid crystal layer 40 in order to stabilize the liquid crystalmolecules 40 a. Therefore, the number of production steps or productioncost is not increased, or the numerical aperture is not reduced.

In such an LCD device 500, each of a plurality of pixel regions, in itsentirety, has sub regions in which the liquid crystal molecules 40 a arealigned in an axially symmetrical manner. Accordingly, the LCD device500 has a high viewing angle characteristic. The response time issufficiently short, and no image sticking phenomenon is exhibited. Theaxially symmetrical alignment is quite stable, and no defectivealignment is generated in a repeated operation test. In this example,the alignment fixing layers 41 a and 41 b are provided on the activematrix substrate 520 and the counter substrate 530. The alignment fixinglayer can be provided in either substrate.

EXAMPLE 6

In the first through fifth examples, the spacers for controlling thethickness of the liquid crystal layer 40 are formed of plastic beads,which are distributed on the active matrix substrate. FIG. 20A shows thealignment of the liquid crystal molecules in a pixel region 100 c whenthe openings 24 a are a distance away from the edges of the pixelelectrode. FIG. 20B shows the alignment of the liquid crystal moleculesin a pixel region 400C when the openings 424 a are along and overlappingthe edges of the pixel electrode. When plastic beads 92 are in the pixelregion 100 c or 400 c, the axially symmetrical alignment of the liquidcrystal molecules in at least one of the sub pixel regions (60 a through60 c in FIG. 20A, 60 a through 60 i in FIG. 20B) may undesirably bedisturbed. In order to prevent the disturbance in the alignment causedby the plastic beads 92, an LCD device in a sixth example according tothe present invention includes a column-like projection formed of apolymer provided in a position in the pixel region at which thecolumn-like projection does not influence the display.

FIGS. 21A through 21D show exemplary active matrix substrates of an LCDdevice in the sixth example. In FIGS. 21A and 21B, the openings 24 a area distance away from the edges of the pixel electrode 24. In FIGS. 21Cand 21D, the openings 424 a are along and overlapping the edges of thepixel electrode 24. As shown in FIGS. 21A through 21D, a column-likeprojection 94 is provided.

The column-like projection 94 shown in FIGS. 21A and 21C is formed in,for example, the following manner.

The active matrix substrate is formed in the same manner as in the firstexample. On the active matrix substrate, a photocurable resin (e.g.,OMR83, Tokyo Ohka Kogyo Co., Ltd.) is applied to a thickness of about 4μm. The photocurable resin is treated with exposure and development tobe partially left in the shape of the column-like projection 94 on aline provided in a peripheral area of the pixel region.

In the case where the storage capacitance common line 76 is formed of alight-blocking material, such as a metal material, the column-likeprojection 94 can be provided above the storage capacitance common line76 as shown in FIGS. 21B and 21D.

FIG. 22A is a top view of a pixel area 100 d of an LCD device includingthe active matrix substrate shown in FIG. 21A or 21B, in which theopenings 24 a are a distance away from the edges of the pixel electrode.FIG. 22B is a top view of a pixel area 400 d of an LCD device includingthe active matrix substrate shown in FIG. 21C or 21D, in which theopenings 424 a are along and overlapping the edges of the pixelelectrode. The views shown in FIGS. 22A and 22B are obtained by apolarized microscope when the LCD devices are supplied with a voltagefor gray scale display.

As shown in FIGS. 22A and 22B, the liquid crystal molecules in thevicinity of the openings 24 a or 424 a are aligned radially around eachopening 24 a or 424 a. The liquid crystal molecules farther from theopening 24 a or 424 a are tilted at a greater angle with respect to theline normal to the surfaces of the vertical alignment layers than theliquid crystal molecules closer to the opening 24 a or 424 a. Thus, theliquid crystal molecules in each of a plurality of sub pixel regions inthe pixel region 100 d or 400 d are aligned in an axially symmetricalmanner.

Accordingly, the LCD device in the sixth example has a high viewingangle characteristic. The response time is sufficiently short, and noimage sticking phenomenon is exhibited. The disturbance in the axiallysymmetrical alignment of the liquid crystal molecules caused when thepixel regions contain plastic beads is not exhibited. The uniformity inthe thickness of the liquid crystal layer is raised, thus improving thedisplay quality.

EXAMPLE 7

In the first through sixth examples, the liquid crystal layer 40 isformed of a nematic liquid crystal material having a negative dielectricanisotropy. In a seventh example according to the present invention, achiral dopant (e.g., S811, Merck & Co., Inc.) is added to such a liquidcrystal material, so that the chiral pitch in the liquid crystal layer40 is about 18 μm. In other words, the chiral dopant is added so thatthe liquid crystal molecules have a twist angle of about 90 degrees,i.e., a spiral pitch about four times the cell thickness, for thefollowing reasons. When the twist angle of the liquid crystal moleculesis about 90 degrees when an electric field is applied, the lightutilization ratio and the color balance for the white display areoptimized as in conventional twisted nematic LCD devices. When theamount of the chiral dopant is excessively small, the twist orientationof the liquid crystal molecules when an electric field is applied may beundesirably unstable. When the amount of the chiral dopant isexcessively large, the vertical alignment of the liquid crystalmolecules when no voltage is applied may be undesirably unstable.

Except for the addition of the chiral dopant, the LCD device in theseventh example has a substantially identical structure with, and can beproduced in a similar method, to the LCD device 100 in the firstexample.

FIG. 23A is a top view of a pixel area 10 e of an LCD device in theseventh example, in which the openings 24 a are a distance away from theedges of the pixel electrode. FIG. 23B is a top view of the pixel area400 e of another LCD device in the seventh example, in which theopenings 424 a are along and overlapping the edges of the pixelelectrode. The views shown in FIGS. 23A and 23B are obtained by apolarized microscope when the LCD devices are supplied with a voltagefor gray scale display.

As shown in FIGS. 23A and 23B, the liquid crystal molecules in thevicinity of the openings 24 a or 424 a are aligned radially around eachopening 24 a or 424 a. The liquid crystal molecules farther from theopening 24 a or 424 a are tilted at a greater angle with respect to theline normal to the surfaces of the vertical alignment layers than theliquid crystal molecules closer to the opening 24 a or 424 a. Thus, theliquid crystal molecules in each of a plurality of sub pixel regions inthe pixel region 100 e or 400 e are aligned in an axially symmetricalmanner.

Accordingly, the LCD device in the seventh example has a high viewingangle characteristic. The response time is sufficiently short, and noimage sticking phenomenon is exhibited. Compared to the LCD device 100in which the liquid crystal layer 40 does not include a chiral dopant,the seventh example provides a brighter image with a smaller dark field.The light transmittance is not reduced even when the pixel electrode 24has a great number of openings or large-sized openings.

EXAMPLE 8

In an eighth example according to the present invention, LCD devicesfurther including an appropriate phase plate for further widening theviewing angle range will be described.

As shown in FIG. 24A, an LCD device 600 includes a pair of polarizers602 a and 602 b in addition to a first substrate 620, a second substrate630 and a liquid crystal layer 640 interposed between the substrates 620and 630. The first substrate 620, the second substrate 630 and theliquid crystal layer 640 can have any structure described in the firstthrough seventh examples. The polarizer 602 a is closer to the displayplane, and the polarizer 602 b is closer to the backlight. The lightabsorbing direction of the polarizer 602 b is the x direction. Adirection vertical to the x direction within the display plane is the ydirection. A direction normal to the display plane is the z direction.

In the LCD device 600 shown in FIG. 24A, a phase plate 604 a is providedbetween the second substrate 630 and the polarizer 602 a. Where therefractive index of the phase plate 604 a is (nx, ny, nz), the phaseplate 602 a has a relationship of nx=ny>nz.

The viewing angle characteristic of the LCD device 600 is improved bysetting a retardation of the phase plate 604 a to be about ½ to{fraction (3/2)} of a retardation of the liquid crystal layer 640. Theretardation of the phase plate 604 a=film thickness (dp) of the phaseplate 604 a×{(nx+ny))/2−nz}. The retardation of the liquid crystal layer640=thickness of the liquid crystal layer 640×(ne−no). A similar effectis obtained by providing the phase plate 604 a between the firstsubstrate 620 and the polarizer 602 b. “ne” represents the refractiveindex of extraordinary rays, and “no” represents the refractive index ofordinary rays.

In an LCD device 650 shown in FIG. 24B, the phase plate 604 a isprovided between the second substrate 630 and the polarizer 602 a, andthe phase plate 604 b is provided between the first substrate 620 andthe polarizer 602 b. Where the refractive index of each of the phaseplates 604 a and 604 b is (nx, ny, nz), the phase plates 602 a and 602 beach have the relationship of nx=ny>nz.

The viewing angle characteristic of the LCD device 650 is improved bysetting a total of the retardations of the phase plates 604 a and 604 bto be about ½ to about {fraction (3/2)} of the retardation of the liquidcrystal layer 640.

FIG. 25A is a graph illustrating the dependency of the lighttransmittance on the viewing angle in the black display state of the LCDdevice 650 including the phase plates 604 a and 604 b (FIG. 24B). Theretardation of the liquid crystal layer is 360 nm (thickness of theliquid crystal layer: 4.5 μm, ne=1.55, no=1.47). The total of theretardations of the phase plates 604 a and 604 b is varied. Thehorizontal axis (viewing angle θ) of FIG. 25A represents the viewingangle with respect to the direction which is 45 degrees with respect tothe polarization axis (i.e., the angle with respect to the directionnormal to the display plane). The vertical axis (transmittance) of FIG.25A represents a value normalized with the light transmittance of airbeing 1. FIG. 25B illustrates values of transmittance plotted withrespect to the retardation. The values of transmittance are obtainedwhen the viewing angle θ is 60 degrees.

As can be appreciated from FIG. 25A, when no phase plate is provided(retardation: 0 nm), the light transmittance is raised (i.e., lightleaks) as the viewing angle θ increases in a direction which is 45degrees offset from the polarization axis. Thus, a satisfactory blackdisplay state is not obtained. When the phase plate 604 a (and/or 604 b)is provided and the retardation thereof {dp×(nx+ny)/2−nz} is set at anappropriate value, the light transmittance is reduced as shown in FIG.25B. Specifically when the total of the retardations of the phase plate604 a and 604 b is about 180 nm (½ of the retardation of the liquidcrystal layer) to about 540 nm ({fraction (3/2)} of the retardation ofthe liquid crystal layer), the increase of the light transmittance isreduced to half or less of the increase of the light transmittanceobtained when no phase plate is provided, at θ=60 degrees.

As described above, where no phase plate is provided, the black displaystate with no voltage being applied is satisfactory when observed in thedirection normal to the display plane as described above. However, in adirection inclined with respect to the normal direction, a phasedifference generated by the liquid crystal layer causes light leakageand thus degradation of the black display. The phase plate or platesshown in FIGS. 24A and 24B compensate for such a phase difference, andthus allows a satisfactory black display state to be provided in a wideviewing angle range. In other words, high contrast images are obtainedin a wide viewing angle range.

FIG. 26A shows an LCD device 700 including a phase plate 606 a providedbetween the second substrate 630 and the polarizer 602 a. FIG. 26B showsan LCD device 750 including a phase plate 606 a provided between thesecond substrate 630 and the polarizer 602 a and a phase plate 606 bprovided between the first substrate 620 and the polarizer 602 b. Thephase plates 606 a and 606 b each have a relationship of nx>ny=nz. Theviewing angle characteristic of the LCD device 750 is improved bysetting a total of retardations of the phase plates 606 a and 606 b tobe about {fraction (1/10)} to about {fraction (7/10)} of a retardationof the liquid crystal layer 640. The retardation of each of the phaseplates 606 a and 606 b is dp×{nx−(ny+nz)/2}. Provision of the phaseplate or plates improves the black display state when observed in theazimuth direction which is 45 degrees offset with respect from the lightabsorbing axis of the polarizers 602 a and 602 b.

FIG. 27A is a graph illustrating the dependency of the lighttransmittance on the viewing angle in the black display state of the LCDdevice 750 including the phase plates 606 a and 606 b (FIG. 26B). Theretardation of the liquid crystal layer is 360 nm (thickness of theliquid crystal layer: 4.5 μm, ne=1.55, no=1.47). The total of theretardations of the phase plates 606 a and 606 b is varied. Theretardation in the direction of the nz axis, i.e., {dp×(nx+ny)/2−nz} ofthe phase plates 606 a and 606 b is fixed at 250 nm. The horizontal axis(viewing angle θ) of FIG. 27A represents the viewing angle with respectto the direction which is 45 degrees with respect to the polarizationaxis (i.e., the angle with respect to the direction normal to thedisplay plane). The vertical axis (transmittance) of FIG. 25 representsa value normalized with the light transmittance of air being 1. FIG. 27Billustrates values of transmittance plotted with respect to theretardation. The values of transmittance are obtained when the viewingangle θ is 60 degrees.

As can be appreciated from FIG. 27A, when no phase plate is provided(retardation: 0 nm), the light transmittance is raised (i.e., lightleaks) as the viewing angle θ increases in a direction which is 45degrees offset from the polarization axis. Thus, a satisfactory blackdisplay state is not obtained. When the phase plate 606 a (and/or 606 b)is provided and the retardation thereof dp×{nx−(ny+nz)/2)} is set at anappropriate value, the light transmittance is reduced as shown in FIG.27B. Specifically when the total of the retardations of the phase plate606 a and 606 b is about 36 nm ({fraction (1/10)} of the retardation ofthe liquid crystal layer) to about 252 nm ({fraction (7/10)} of theretardation of the liquid crystal layer), the transmission is belowabout 0.03. Accordingly, the increase of the light transmittance islower than the increase of the light transmittance obtained when nophase plate is provided, at θ=60 degrees.

The two types of phase plates, i.e., 604 a or 604 b in FIGS. 24A and 24Band 606 a or 606 b in FIGS. 26A and 26B can be combined together asshown in FIG. 28A. The two types of phase plates can be combined in anyother combination. A similar viewing angle characteristic is obtained byproviding a biaxial phase plate 610 a (FIG. 28B) or biaxial phase plates610 a and 610 b (FIG. 28C). The biaxial phase plates 610 a and 610 bprovide a substantially equal refractive index anisotropy to therefractive index anisotropy obtained by the two monoaxial phase plates.Use of one biaxial phase plate in lieu of two monoaxial phase platesreduces the number of production steps.

In the first through eighth examples, a vertical alignment mode liquidcrystal layer is used. The present invention is not limited to such astructure. A similar effect is obtained when a horizontal alignment mode(e.g., twisted nematic or super twisted nematic mode) liquid crystallayer is used.

In the first through eighth examples, the transmission active matrixsubstrate LCD devices are described. The present invention is notlimited to such a type of LCD devices and is widely applicable toreflective LCD devices and simple matrix LCD devices.

As described above, according the present invention, an LCD devicehaving a high viewing angle characteristic and preventing an imagesticking phenomenon is provided. The liquid crystal molecules arealigned in an axially symmetrical manner uniformly and stably in aplurality of sub pixel regions included in each of pixel regions. Suchalignment of the liquid crystal molecules provides a wide viewing anglerange to improve the display quality, and a high speed response. The LCDdevice according to the present invention can be produced withoutrequiring any additional step to the conventional production method, andthus does not raise the production cost.

According to the present invention, the alignment of the liquid crystalmolecules is prevented from becoming unstable due to the lateralelectric field generated by scanning lines and signal lines (bus lines)provided for connecting the active devices.

According to the present invention, generation of disclination at nearedges of the pixel electrode is suppressed.

According to the present invention, the alignment of the liquid crystalmolecules is stable, which provides a bright display.

An LCD device according to the present invention is applicable inmonitors of, for example, computers, wordprocessors, car navigationsystems, and TVs.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A liquid crystal display device, comprising: afirst substrate; a second substrate; and a liquid crystal layerInterposed between the first substrate and the second substrate, thefirst and second substrates respectively including a first electrodelayer and a second electrode layer facing the liquid crystal layer, thefirst and second electrodes layers being provided for applying a voltageto the liquid crystal layer, and wherein the first electrode layerincludes a plurality of pixel electrodes arranged in a shape of a matrixand a plurality of openings are regularly located per pixel in the firstor second electrode layer, some being formed overlapping edges or atcomers of the pixel electrodes.
 2. A liquid crystal display deviceaccording to claim 1, wherein each of the pixel electrodes is connectedto a scanning line and a signal line through a switching device, and thesecond electrode is a counter electrode facing the plurality of pixelelectrodes each of which includes a plurality of openings which arearranged regularly to each of the plurality of pixel electrodes.
 3. Aliquid crystal display device according to claim 2, wherein all shapesof the openings are congruent to each other.
 4. A liquid crystal displaydevice according to claim 2, wherein a shape to be regulated by lineslinking centers of the closest two openings is a polygon having arotational symmetry.
 5. A liquid crystal display device according toclaim 4, wherein a shape to be regulated by lines linking centers of theclosest two openings is congruent to each other.
 6. A liquid crystaldisplay device according to claim 4, wherein a recession is formed at acenter of shape to be regulated by lines linking centers of the closesttwo openings.
 7. A liquid crystal display device according to claim 4,wherein the liquid crystal layer is formed by a liquid crystal materialhaving a negative dielectric anisotropy.
 8. A liquid crystal displaydevice according to claim 1, wherein the liquid crystal layer includes achiral dopant.
 9. A liquid crystal display device according to claim 1,further comprising a pair of polarizers interposing therebetween thefirst substrate and the second substrate and at least one mono-axialphase plate of a negative refractive index anisotropy.
 10. A liquidcrystal display device according to claim 9, wherein a retardation ofthe mono-axial phase plate having a negative refractive index anisotropyis set about {fraction (2/1)} to {fraction (3/2)} of a retardation ofthe liquid crystal layer.
 11. A liquid crystal display device accordingto claim 9, wherein two types of the phase plate are provided incombination between the pair of polarizers and the first and secondsubstrates.
 12. A liquid crystal display device according to claim 11,wherein two sheets of the mono-axial phase plates are provided incombination between the pair of polarizers and the first and secondsubstrates.
 13. A liquid crystal display device according to claim 9,wherein the two sheets of the mono-axial phase plates are provided incombination between the pair of polarizers and the first and secondsubstrates.
 14. A liquid crystal display device according to claim 13,wherein the two sheets of the mono-axial phase plates are a positivemono-axial phase plate and a negative mono-axial phase plate.
 15. Aliquid crystal display device according to claim 1, further comprising apair of polarizers interposing therebetween the first substrate and thesecond substrate, and at least on mono-axial phase plate of a positiverefractive index anisotropy.
 16. A liquid crystal display deviceaccording to claim 15, wherein a retardation of the mono-axial phaseplate having a positive refractive index anisotropy is set at about{fraction (1/10)} to {fraction (7/10)} of the retardation of the liquidcrystal layer.
 17. A liquid crystal display device according to claim15, wherein two types of the phase plate are provided in combinationbetween the pair of polarizers and the first and second substrates. 18.A liquid crystal display device according to claim 15, wherein twosheets of the mono-axial phase plates are provided in combinationbetween the pair of polarizers and the first and second substrates. 19.A liquid crystal display device according to claim 15, wherein twosheets of mono-axial phase plates are provided in combination betweenthe pair of polarizers of the first and second substrates.
 20. A liquidcrystal display device according to claim 19, wherein the two sheets ofthe mono-axial phase plates are a positive mono-axial phase plate and anegative mono-axial phase plate.
 21. A liquid crystal display deviceaccording to claim 1, further comprising a pair of polarizersinterposing therebetween the first substrate and the second substrate,and at least one sheet of biaxial phase plate being located between atleast one of the polarizers and the adjacent substrate.
 22. A liquidcrystal display device according to claim 21, wherein two sheets of thebiaxial phase plate are provided in combination interposing between thepair of polarizers of the first and second substrates.
 23. A liquidcrystal display device, comprising: a first substrate; a secondsubstrate; and a liquid crystal layer interposed between the firstsubstrate and the second substrate, the first and second substratesrespectively including a first electrode layer and a second electrodelayer facing the liquid crystal layer, the first and second electrodeslayers being provided for applying a voltage to the liquid crystallayer, and a plurality of openings which are regularly located in thefirst electrode layer or the second electrode layer, wherein the firstelectrode layer includes a plurality of pixel electrodes arranged in ashape of matrix each of which is connected to a scanning line and asignal line through a switching device, and the second electrode layerbeing a counter electrode facing the plurality of pixel electrodes eachof which includes plurality of openings which are arranged regularly toeach of the plurality of pixel electrodes, and wherein at least one edgeof a polygon including a rotational symmetry to be regulated by lineslinking contours of the closest two opening is identical to at least oneedge of the pixel electrodes.